The present invention is directed to a method and catalyst system for producing aromatic carbonates and, more specifically, to a method and catalyst system for producing diaryl carbonates through the carbonylation of aromatic hydroxy compounds.
Aromatic carbonates find utility, inter alia, as intermediates in the preparation of polycarbonates. For example, a popular method of polycarbonate preparation is the melt transesterification of aromatic carbonates with bisphenols. This method has been shown to be environmentally superior to previously used methods which employed phosgene, a toxic gas, as a reagent and chlorinated aliphatic hydrocarbons, such as methylene chloride, as solvents.
Various methods for preparing aromatic carbonate monomers have been previously described in the literature and/or utilized by industry. A method that has enjoyed substantial popularity in the literature involves the direct carbonylation of aromatic hydroxy compounds with carbon monoxide and oxygen. In general, practitioners have found that the carbonylation reaction requires a rather complex catalyst system. For example, in U.S. Pat. No. 4,187,242, which is assigned to the assignee of the present invention, Chalk reports that a carbonylation catalyst system should contain a Group 8, 9, or 10 metal, such as ruthenium, rhodium, palladium, osmium, iridium, platinum, or a complex thereof. Further refinements to the carbonylation reaction include the identification of organic co-catalysts, such as terpyridines, phenanthrolines, quinolines and isoquinolines in U.S. Pat. No. 5,284,964 and the use of certain halide compounds, such as quaternary ammonium or phosphonium halides in U.S. Pat. No. 5,399,734, both patents also being assigned to the assignee of the present invention.
The economics of the carbonylation process are strongly dependent, inter alia on the number of moles of aromatic carbonate produced per mole of Group 8, 9, or 10 metal utilized (i.e. xe2x80x9ccatalyst turnoverxe2x80x9d). Consequently, much work has been directed to the identification of efficacious inorganic co-catalysts that increase catalyst turnover. In U.S. Pat. No. 5,231,210, which is also assigned to General Electric Company, Joyce et al. report the use of a cobalt pentadentate complex as an inorganic co-catalyst (xe2x80x9cIOCCxe2x80x9d). In U.S. Pat. No. 5,498,789, Takagi et al. report the use of lead as an IOCC. In U.S. Pat. No. 5,543,547, Iwane et al. report the use of trivalent cerium as an IOCC. In U.S. Pat. No. 5,726,340, Takagi et al. report the use of lead and cobalt as a binary IOCC system. In co-pending application Ser. No. 09/677,487, filed Oct. 2, 2000, Soloveichik et al. report the use of lead and copper as a binary IOCC system.
Further complexity was added to carbonylation catalyst systems by Buysch et al. in U.S. Pat. No. 5,502,232, which teaches the use of a quaternary salt, a co-catalyst, a base, and a desiccant in a supported Pd-based carbonylation system. In U.S. Pat. No. 5,821,377, Buysch et al. report the use of said aforementioned catalyst system with the Pd and the co-catalyst provided on the same support.
The literature is virtually silent, however, as to the role of various catalyst system components, such as IOCCs and onium halides for example, in the carbonylation reaction (i.e., the reaction mechanism). Accordingly, meaningful guidance regarding the identification of additional catalyst systems is cursory at best. It would be desirable to identify catalyst systems that would minimize consumption of costly components (e.g., palladium and onium halides) or perhaps that would omit these components. It would also be desirable to minimize the aforementioned consumption of costly components while increasing selectivity toward desirable products and minimizing formation of undesirable by products (e.g., 2-and 4-bromophenols). Unfortunately, due to the lack of guidance in the literature, the identification of effective carbonylation catalyst systems has become a serendipitous exercise.
As the demand for high performance plastics continues to grow, new and improved methods of providing product more economically are needed to supply the market. In this context, various processes and catalyst systems are constantly being evaluated; however, the identities of improved and or additional effective catalyst systems for these processes continue to elude the industry. Consequently, a long felt, yet unsatisfied need exists for new and improved methods and catalyst systems for producing aromatic carbonates and the like.
Accordingly, the present invention is directed to a method and catalyst system for producing aromatic carbonates. In one embodiment, the present invention provides a carbonylation catalyst system comprising an effective amount of at least one Group 8, 9, or 10 metal source; an effective amount of at least one bromide composition; an effective amount of at least one activating organic solvent; an effective amount of a combination of inorganic co-catalysts comprising at least one titanium source and at least one copper source; and an effective amount of at least one base.
In another embodiment, the present invention provides a method for carbonylating aromatic hydroxy compounds, said method comprising the step of: contacting at least one aromatic hydroxy compound with oxygen and carbon monoxide in the presence of a carbonylation catalyst system comprising an effective amount of at least one Group 8, 9, or 10 metal source; an effective amount of at least one bromide composition; an effective amount of at least one activating organic solvent; an effective amount of a combination of inorganic co-catalysts comprising at least one titanium source and at least one copper source; and an effective amount of at least one base.
Various features, aspects, and advantages of the present invention will become more apparent with reference to the following description and appended claims.